1. Field of the Invention
The present invention relates to a colloid solution of metal nanoparticles, metal-polymer nanocomposites, and methods for preparing the same, and more particularly, to a metal colloid solution and metal-polymer nanocomposites prepared using a variety of polymeric stabilizers and having a uniform particle diameter, and methods for preparing the same.
2. Description of the Related Art
Recently, a method for preparing a colloidal dispersion of silver nanoparticles using gamma rays and appropriate stabilizers, such as polyvinyl alcohol and sodium dodecyl sulfate (SDS) was disclosed (Nature 1985, 317, 344; Materials Letters 1993, 17, 314). The preparation method using gamma rays was reported to provide uniform diameter distribution of the silver nanoparticles. The metal nanoparticles prepared by those methods were known to have a size of from about 8 nm to tens of nanometers from the outstanding research reports. However, the metal nanoparticles are prepared by these methods not so desirable in terms of particle diameter and shape uniformity.
It is important to obtain pure silver particles having a uniform shape within a narrow distribution range of particle diameters for industrial applications. For example, ultrafine silver particles are essential materials in the electronics applications, for example, for conductive ink and paste and adhesive applied in the manufacture of a variety of electronic parts.
As described above, there is a need for a new method for preparing metal nanoparticles having a uniform size and shape. In addition, good dispersion stability for preventing agglomeration of metal nanoparticles in a dispersion medium is another consideration for industrial applications. For diversified industrial applications, miscibility with a variety of organic solvents, plasticizers, and resins is required to prepare a metal colloid solution in a non-aqueous medium.
A variety of methods for preparing a solid phase of polymer-metal nanocomposites were suggested (Polym. Composites 1996, 7, 125; J. Appl. Polym. Sci. 1995, 55, 371; J. Appl. Polym. Sci. 1996, 60, 323). These methods involve two steps: (1) polymerization of monomer particles and (2) reduction of metal ions in a polymerized medium. However, the separate polymerization and reduction processes cause non-uniform size distribution of the metal nanoparticles in the polymerized medium.
To solve this problem, a method for preparing silver-polymer nanocomposites using gamma rays was developed (Chem. Commun. 1997, 1081). In the method, a silver salt is dissolved in water, mixed with acrylic amide as a water-soluble monomer, and subjected to gamma-rays irradiation to prepare the silver-polymer nanocomposites. Here, reduction of silver ions coincides with polymerization of the monomer, so that the metal nanoparticles are comparatively uniformly dispersed in the polymerized medium.
However, this method also cannot be applied when using a variety of water-insoluble monomers. To overcome the limitation encountered when using an aqueous medium, the preparation of silver-polymer nanocomposites from a water-in-oil (W/O) emulsion was reported (Chem. Commun. 1998, 941), wherein toluene was used for the oil phase.
According to the method, since a variety of water-insoluble monomers can be applied, various kinds of metal-polymer nanoparticles can be prepared. However, the use of excess toluene for the oily medium, up to about 5 times the amount of water, causes environmental concerns. In addition, a safe working environment is not guaranteed due to a high risk of explosion in its preparation.